Transient stability limit evaluation method and system for new energy flexible direct delivery system

Abstract

The invention provides a transient stability limit evaluation method and system of a new energy flexible direct current delivery system, and relates to the technical field of transient stability quantitative evaluation of a new energy power system, and the method comprises the steps: building a transient linear model of new energy and flexible direct current multiple devices, and a system nonlinear model; constructing a system state matrix according to the linearization model, screening the type-I balance points through the state matrix, and calculating a first-order parameter matrix of a hypertangent plane of each target type-I balance point; calculating a Hessian matrix according to the nonlinear model, and calculating a second-order parameter matrix of the hypertangent plane of the type I balance point of each target by using the Hessian matrix; and according to the first-order parameter matrix and the second-order parameter matrix, constructing a corresponding hyper-tangent plane equation, in combination with the fault trajectory, determining the intersection point of the trajectory and a hyper-tangent plane, calculating the fault limit clearing time, and evaluating the transient stability margin of the system. According to the method, the fault clearing time of the system under different types of faults can be accurately calculated, and the transient stability of the new energy flexible direct delivery system can be accurately evaluated.

Description

Technical Field

[0001] The present disclosure relates to the technical field of quantitative evaluation of transient stability of new energy power systems, and in particular to a transient stability limit evaluation method and system for a new energy flexible direct current transmission system. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.

[0003] Under the current new situation of vigorously promoting clean energy power generation such as hydropower, photovoltaics, and wind power, building comprehensive clean energy power generation bases such as hydropower, photovoltaics, and wind power is an important measure in the field of energy and power. With the rapid growth of new energy represented by wind power and photovoltaics, the penetration rate of new energy in the power grid continues to increase. Since large-scale new energy bases are far away from the load center, in order to meet the urgent needs of long-distance power transmission of large-scale new energy bases, the development of ultra-high voltage long-distance power transmission technology is a strategic choice for power development. Among them, the flexible direct current transmission system has obvious advantages in the fields of power grid interconnection and large-capacity long-distance power transmission. Large-scale new energy transmission through flexible direct current will be the main technical solution adopted by new energy bases such as remote areas and Shagohuang. However, the large-scale new energy transmission system through flexible direct current has a high penetration rate of power electronic equipment, strong interaction, and small transient stability margin, which is prone to transient instability accidents, seriously threatening the safe operation of the power grid at the sending end and the reliable absorption of new energy.

[0004] At present, for the transient stability problem of single renewable energy grid-connected system, there have been studies using a variety of methods to analyze the transient stability problem of single renewable energy grid-connected system, such as EAC analysis, Lyapunov function method, energy function method, sum of square (SOS) estimation method, phase diagram analysis and bifurcation analysis. However, since the dynamic characteristics of renewable energy power electronic equipment are significantly different from those of synchronous machines, the energy function construction method based on the mathematical equations and dynamic characteristics of synchronous machines is difficult to apply. Therefore, it is very challenging to directly apply the existing analysis method based on synchronous machines to the transient stability evaluation of multiple power electronic equipment systems. On the other hand, some studies have proposed some transient stability analysis and evaluation methods based on artificial intelligence and numerical simulation. However, compared with theoretical analysis methods, numerical simulation methods are time-consuming and cannot provide operators with relevant indicators such as transient stability margin. Therefore, for renewable energy flexible direct current transmission systems with multiple power electronic equipment, the transient stability evaluation method is still imperfect. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a transient stability limit evaluation method and system for a new energy via flexible direct current transmission system, realizes quantitative evaluation of transient stability of a new energy via flexible direct current transmission system based on second-order estimation, and simultaneously considers the conditions of new energy and flexible direct current equipment, quantitatively calculates the limit removal time to ensure system stability after a transient large disturbance fault occurs, and guides the parameter setting of control and protection devices of a large-scale new energy base via flexible direct current transmission system.

[0006] According to some embodiments, the present disclosure adopts the following technical solutions:

[0007] The transient stability limit evaluation method of the new energy transmission system through flexible direct current includes:

[0008] Obtain the primary wiring topology of the new energy transmission system through flexible direct current, and establish a transient reduced-order linearization model of the new energy equipment, a transient reduced-order linearization model of flexible direct current multi-equipment, and a nonlinearization model of the new energy transmission system through flexible direct current according to the primary wiring topology;

[0009] A system state matrix is ​​constructed according to the linearized model, a group of type-one equilibrium points is preliminarily determined according to the nonlinearized model, each target type-one equilibrium point is screened from the group of type-one equilibrium points through the system state matrix, and the first-order parameter matrix of the hypersection of each target type-one equilibrium point is calculated;

[0010] Calculate the Hessian matrix according to the nonlinear model, and use the Hessian matrix to calculate the second-order parameter matrix of the hypersection of each target type-one equilibrium point;

[0011] The corresponding hypersection surface equation is constructed according to the first-order parameter matrix and the second-order parameter matrix. The corresponding hypersection surface equation is constructed according to the fault trajectory and the first-order parameter matrix and the second-order parameter matrix. The intersection of the fault trajectory and the hypersection surface equation is determined, and the minimum value of the time of all the obtained intersection points is taken as the limit resection time of the fault.

[0012] According to some embodiments, the present disclosure adopts the following technical solutions:

[0013] The transient stability limit evaluation system of the new energy transmission system through flexible direct current includes:

[0014] A model building module is used to obtain the primary wiring topology of the new energy transmission system through flexible direct current, and to establish a transient reduced-order linearization model of the new energy equipment, a transient reduced-order linearization model of the flexible direct current equipment, and a nonlinear model of the new energy transmission system through flexible direct current according to the primary wiring topology;

[0015] The first-order parameter determination module is used for the first-order parameter determination module, which is used to construct a system state matrix according to the linearized model, preliminarily determine a group of type-one equilibrium points according to the nonlinearized model, select each target type-one equilibrium point from the group of type-one equilibrium points through the system state matrix, and calculate the first-order parameter matrix of the hypersection of each target type-one equilibrium point;

[0016] A second-order parameter determination module is used to calculate the Hessian matrix according to the nonlinear model, and use the Hessian matrix to calculate the second-order parameter matrix of each target type-one equilibrium point hypersection;

[0017] The quantitative evaluation module is used to construct the corresponding hyper-section surface equation according to the first-order parameter matrix and the second-order parameter matrix, to construct the corresponding hyper-section surface equation according to the fault trajectory and the first-order parameter matrix and the second-order parameter matrix, to determine the intersection of the fault trajectory and the hyper-section surface equation, and to take the minimum value of the time of all the obtained intersections as the limit removal time of the fault.

[0018] According to some embodiments, the present disclosure adopts the following technical solutions:

[0019] A non-transitory computer-readable storage medium is used to store computer instructions. When the computer instructions are executed by a processor, the transient stability limit evaluation method of the new energy flexible direct current transmission system is implemented.

[0020] According to some embodiments, the present disclosure adopts the following technical solutions:

[0021] An electronic device comprises: a processor, a memory and a computer program; wherein the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device is running, the processor executes the computer program stored in the memory so that the electronic device executes the transient stability limit evaluation method of the new energy flexible direct current transmission system.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The transient stability limit evaluation method of the new energy direct current transmission system disclosed in the present invention provides a high accuracy of the limit removal time under various faults, which is beneficial to the online identification and judgment of the transient stability limit conditions of the direct current transmission system of a large-scale new energy base, timely isolation of faults, and prevention of cascading failures. It can also be used to study the influence of factors such as network connection structure, system operating conditions, and controller parameters on the system fault limit removal time. On the whole, it can improve the accurate calculation and stability evaluation of the fault limit removal time of the direct current transmission system of a large-scale new energy base.

[0024] The transient stability limit evaluation method of the new energy via flexible direct current transmission system disclosed in the present invention adopts a simple model, has low numerical calculation requirements, is applicable to symmetrical and asymmetrical faults, and is easy to be applied to the flexible direct current transmission system of large-scale new energy bases.

[0025] The transient stability limit evaluation method of the new energy via flexible direct current transmission system disclosed in the present invention can accurately calculate the system fault removal time under different types of faults, realize the quantitative evaluation of transient stability, and further study the influence of factors such as network connection structure, system operating conditions, and controller parameters on the system fault limit removal time; the calculation process is simple, the calculation method is clear, and the calculation results are easy to use, which is convenient for on-site application in existing large-scale new energy via flexible direct current transmission system scenarios, and has great advantages in the quantitative evaluation of transient stability and the planning and design considering transient stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings constituting a part of the present disclosure are used to provide a further understanding of the present disclosure. The illustrative embodiments of the present disclosure and their descriptions are used to explain the present disclosure and do not constitute an improper limitation on the present disclosure.

[0027] Figure 1 This is a flow chart of a transient stability limit evaluation method for a new energy flexible direct current transmission system according to an embodiment of the present disclosure;

[0028] Figure 2 Schematic diagram of the network topology of the new energy flexible direct current transmission system according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0029] The present disclosure is further described below in conjunction with the accompanying drawings and embodiments.

[0030] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further explanation of the present disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present disclosure belongs.

[0031] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0032] Example 1

[0033] In one embodiment of the present disclosure, a transient stability limit evaluation method for a new energy system via flexible direct current transmission is provided, which is also a transient stability quantitative evaluation method for a new energy system via flexible direct current transmission based on second-order estimation, including four steps of system linear and nonlinear modeling, type I equilibrium point determination and first-order parameter calculation, second-order parameter calculation, and limit removal time determination, such as Figure 1 As shown, the specific process steps include:

[0034] Step 1: Obtain the primary connection topology of the flexible direct current transmission system for renewable energy, and establish transient reduced-order linear models of renewable energy and flexible direct current multi-devices, as well as a nonlinear model of the flexible direct current transmission system for renewable energy based on the primary connection topology;

[0035] Step 2: Construct a system state matrix based on the linearized model, preliminarily determine a group of type-one equilibrium points based on the nonlinearized model, select the target type-one equilibrium point from the group of type-one equilibrium points through the system state matrix, and calculate the first-order parameter matrix of the hypersection of each target type-one equilibrium point;

[0036] Step 3: Calculate the Hessian matrix according to the nonlinear model, and use the Hessian matrix to calculate the second-order parameter matrix of the hypersection of each target type-one equilibrium point;

[0037] Step 4: Construct the corresponding hypersection surface equation according to the first-order parameter matrix and the second-order parameter matrix, construct the corresponding hypersection surface equation according to the fault trajectory and the first-order parameter matrix and the second-order parameter matrix, determine the intersection of the fault trajectory and the hypersection surface equation, and take the minimum value of all the obtained intersection times as the limit resection time, so as to obtain the limit resection time of the fault.

[0038] As an embodiment, in order to accurately judge the transient limit conditions under the failure of new energy equipment and facilitate computer implementation and field engineering application, the specific implementation process of a transient stability limit evaluation method of a new energy flexible direct current transmission system disclosed in the present invention is as follows:

[0039] Step 1: Establish linear and nonlinear models of the system

[0040] Specifically, by acquiring basic data such as controller parameters of new energy and flexible DC equipment, system operating conditions, etc., transient reduced-order nonlinear models (nonlinear equations) and linear models (linear state equations) of new energy equipment and flexible DC equipment are established.

[0041] by Figure 2 Take the system shown in the figure as an example, the new energy of the sending end system is connected to the large power grid, and part of the power is sent out through the flexible DC equipment. Among them, the new energy and the flexible DC are nodes, which are described by nonlinear / linear differential equations; the power transmission line is a network, which is described by algebraic equations (admittance matrix or impedance matrix).

[0042] Furthermore, when establishing the transient order reduction linearization model of new energy equipment, only the phase-locked loop (PLL) dynamics are considered. The new energy equipment is externally characterized by a current source. The transient order reduction linearization model of the new energy equipment is composed of differential equations and input and output interface equations, namely:

[0043]

[0044] The first small formula in the above equation is the input equation, and the input variable u of the new energy node is tq The terminal voltage U is determined by the network topology t The imaginary part of , Im() represents the real part. The differential equation represents the dynamics of the PLL, x pll Represent the PLL angle and integrator variable, k p,pll ,k i,pll is the PI controller parameter of PLL; i dref ,i qref They respectively represent the d-axis and q-axis current reference values ​​of new energy equipment. It represents the angle between the d-axis and q-axis current reference values, which is equal to arctan(i qref / i dref ). j is an imaginary unit. Among them, the fourth small formula is the output equation representing the characteristics of the controlled current source of the new energy device. At the same time, the linearization model of the new energy device can be obtained as follows:

[0045]

[0046] Furthermore, when establishing the transient reduction linearization model of the flexible DC device, only the virtual synchronous control link is considered. The flexible DC device externally exhibits voltage source characteristics. The transient reduction linearization model of the flexible DC device consists of differential equations and input-output interface equations, specifically:

[0047]

[0048] Among them, the first small formula is the input equation, that is, the input variable of the flexible DC node is the electromagnetic power P e ; Re() represents the real part. The state variables δ, ω represent the angle and frequency of the virtual synchronous generator (VSG), J, D are the inertia and damping control parameters of the VSG control, P e is the input electromagnetic power, P ref is the power reference value controlled by VSG. The fourth formula is the output equation. The output voltage E of the flexible DC device is the given voltage reference value E. ref , the phase δ is determined by VSG control. e is a natural constant, ejθ represents a complex number with an amplitude of 1 and an angle of θ. At the same time, the linearization model of the flexible direct current device can be obtained as follows:

[0049]

[0050] The system state matrix is ​​constructed according to the linearized model, including: the transient reduced-order linearized model of the combined new energy equipment, the transient reduced-order linearized model of the flexible DC equipment and the network equation (algebraic equation of the transmission line), and the system state matrix can be obtained.

[0051] According to the primary connection topology, a nonlinear model of the new energy transmission system through flexible direct current is established, including the nonlinear model of the new energy equipment and the flexible direct current equipment and the network equation, and the nonlinear model of the new energy transmission system through flexible direct current is obtained. Among them, the nonlinear equations of the nodes (flexible direct current equipment and new energy equipment) and the algebraic equations of the network (power transmission line) constitute the nonlinear equations of the system; the linear equations of the nodes (flexible direct current equipment and new energy equipment) and the algebraic equations of the network (power transmission line) constitute the linear model of the system.

[0052] Step 2: Determine the type I equilibrium point and calculate the first-order parameter matrix;

[0053] Specifically, a set of type I equilibrium points is preliminarily determined based on the nonlinear equation, including:

[0054] A set of type-one equilibrium points is preliminarily determined according to the nonlinear model, including: based on the definition that a type-one equilibrium point has only one unstable characteristic root, the unstable characteristic root of the nonlinear model is preliminarily calculated as the type-one equilibrium point.

[0055] Then, according to the definition of a type-one equilibrium point (i.e., there is only one unstable eigenvalue), the target type-one equilibrium point is screened from a group of type-one equilibrium points through the system state matrix, and the first-order parameter matrix of the hypersection of each target type-one equilibrium point is calculated, including: screening the initially obtained type-one equilibrium points through the system state matrix, and from the initially determined type-one equilibrium points, calculating the eigenvalues ​​according to the system state matrix to determine the target type-one equilibrium point; calculating the left eigenvectors corresponding to the unstable eigenroots of the type-one equilibrium points to obtain the first-order parameter matrix of the hypersection equation.

[0056] Specifically, the initially obtained type-I equilibrium points are screened through the obtained system state matrix, and the equilibrium points that meet the definition are screened out from the initially determined type-I equilibrium points (the eigenvalues ​​are calculated according to the aforementioned system state matrix), and the target type-I equilibrium points are determined. At the same time, the left eigenvector corresponding to the unstable eigenroot of the type-I equilibrium point is calculated to obtain the first-order parameter matrix K of the hypersection surface. i ,Right now:

[0057]

[0058] Among them, y i T is the left eigenvector corresponding to the unstable eigenroot of the i-th type-I equilibrium point.

[0059] Step 3: Second-order parameter matrix calculation

[0060] Specifically, according to the definition of the system nonlinear equation and the Hessian Matrix, that is, the Hessian Matrix is ​​a square matrix composed of the second-order partial derivatives of a multivariate function, the calculated Hessian matrix H i for:

[0061]

[0062] The second-order parameter matrix of the hypersection of each target type-one equilibrium point is calculated using the Hessian matrix to satisfy:

[0063]

[0064] in, The symbol represents the Kronecker tensor product, V c is the column stack map operation of the matrix, is the inverse operation of the matrix column stack map operation, I n represents the n-dimensional identity matrix. The coefficient matrices C and H are the intermediate calculation matrices. J is the system state matrix. H i is the Hessian matrix, y i is the left eigenvector corresponding to the unstable eigenvalue of the i-th type I equilibrium point, and μ is the value of the corresponding unstable eigenvalue.

[0065] Step 4: Determine the limit resection time;

[0066] Specifically, according to the first-order parameter matrix and the second-order parameter matrix of the hypersection, the hypersection equation F corresponding to the i-th type-one equilibrium point is i (x) can be expressed as:

[0067]

[0068] Among them, x is the state variable fault trajectory, x u,i is the ith type-one equilibrium point and is a row vector. i T is the transpose of the left eigenvector corresponding to the unstable eigenroot of the i-th type-I equilibrium point.

[0069] At the same time, the corresponding hypersection surface equation is constructed according to the fault trajectory and the first-order parameter matrix and the second-order parameter matrix, and the intersection point of the fault trajectory and the hypersection surface equation is determined, including: bringing the fault trajectory into any hypersection surface equation, when the function F of the hypersection surface equation iWhen the sign of the value of changes, it is considered that the fault trajectory passes through this hyper-tangent plane, that is, it satisfies:

[0070]

[0071] Among them, t i is the time corresponding to the intersection of the i-th target type-one equilibrium point and the fault trajectory in the hypersection equation, and Δt is the time step of the fault trajectory. Therefore, the minimum value of the time corresponding to all the obtained intersection points is taken as the limit removal time, which satisfies:

[0072] t c =min(t 1 ,t 2 ,...,t i )

[0073] Among them, t c is the final determined fault limit clearing time, which is used as one of the evaluation indicators of system stability to evaluate the margin of system transient stability. c The larger the value, the better the stability and the larger the stability margin. c The smaller it is, the worse the system stability is and the smaller the stability margin is.

[0074] Simulation experiment

[0075] The present disclosure uses equivalent grid voltage drop, three-phase short circuit fault and two-phase short circuit fault to detect the effectiveness of the method described in the present disclosure, and verifies the accuracy of the method described in the present disclosure by comparing the limit removal time / angle calculated by the method described in the present disclosure with the time domain simulation calculation results. Taking the voltage drop fault as an example, when the bus voltage drops from 1.0pu to 0.68pu and then recovers to 1.0pu, the fault limit removal time obtained by numerical simulation is 0.157s, and the limit removal time obtained by the hypercut plane method considering only the first-order linear term is 0.161s, with a relative error of 2.55%, and the limit removal time obtained by the method described in the present disclosure considering the second-order coefficient is 0.158s, with a relative error of 1.27%. When a three-phase short circuit fault occurs at the common connection point of the system, the fault limit removal time obtained by numerical simulation is 0.070s, and the limit removal time obtained by the hypertangent plane method considering only the first-order linear term is 0.074s, with a relative error of 5.71%, while the limit removal time obtained by the method described in the present disclosure considering the second-order coefficient is 0.073s, with a relative error of 4.29%. Under other faults, the method described in the present disclosure and the simulation calculation results are shown in Tables 1 and 2. The calculation results show that the method described in the present disclosure can obtain relatively accurate results under different fault types.

[0076] Table 1 Comparison of limit removal time obtained by different methods when voltage drops

[0077]

[0078] Table 2 Comparison of the limit removal time obtained by different methods under short circuit fault

[0079]

[0080] In summary, the method disclosed in the present invention can accurately calculate the system fault removal time under different types of faults, realize the quantitative evaluation of transient stability, and further study the influence of factors such as network connection structure, system operating conditions, and controller parameters on the system fault limit removal time. The calculation process described in the present invention is simple, the calculation method is clear, and the calculation results are easy to use, which is convenient for on-site application in existing large-scale new energy through flexible direct current transmission system scenarios, and has great advantages in the quantitative evaluation of transient stability and planning and design considering transient stability. The present invention also provides a method for quantitative evaluation of transient stability of new energy through flexible direct current transmission system based on second-order estimation, which is used to implement the above-mentioned new energy through flexible direct current transmission transient fault limit removal time evaluation method.

[0081] Example 2

[0082] In one embodiment of the present disclosure, a transient stability limit evaluation system for a new energy flexible direct current transmission system is provided, comprising:

[0083] A model building module is used to obtain the primary wiring topology of the new energy transmission system through flexible direct current, and to establish a transient reduced-order linearization model of the new energy equipment, a transient reduced-order linearization model of the flexible direct current equipment, and a nonlinear model of the new energy transmission system through flexible direct current according to the primary wiring topology;

[0084] A first-order parameter determination module is used to construct a system state matrix according to a linearized model, preliminarily determine a group of type-one equilibrium points according to a nonlinearized model, select each target type-one equilibrium point from the group of type-one equilibrium points through the system state matrix, and calculate the first-order parameter matrix of the hypersection of each target type-one equilibrium point;

[0085] A second-order parameter determination module is used to calculate the Hessian matrix according to the nonlinear model, and use the Hessian matrix to calculate the second-order parameter matrix of each target type-one equilibrium point hypersection;

[0086] The quantitative evaluation module is used to construct the corresponding hyper-section surface equation according to the first-order parameter matrix and the second-order parameter matrix, to construct the corresponding hyper-section surface equation according to the fault trajectory and the first-order parameter matrix and the second-order parameter matrix, to determine the intersection of the fault trajectory and the hyper-section surface equation, and to take the minimum value of the time of all the obtained intersections as the limit removal time of the fault.

[0087] Example 3

[0088] In one embodiment of the present disclosure, a non-transitory computer-readable storage medium is provided, wherein the non-transitory computer-readable storage medium is used to store computer instructions. When the computer instructions are executed by a processor, the transient stability limit evaluation method of the new energy flexible direct current transmission system is implemented.

[0089] Example 4

[0090] In one embodiment of the present disclosure, an electronic device is provided, including: a processor, a memory, and a computer program; wherein the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device is running, the processor executes the computer program stored in the memory, so that the electronic device executes the transient stability limit evaluation method of the new energy flexible direct current transmission system.

[0091] The present disclosure is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present disclosure. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0092] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0093] Although the above describes the specific implementation methods of the present disclosure in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present disclosure. Technical personnel in the relevant field should understand that on the basis of the technical solution of the present disclosure, various modifications or variations that can be made by those skilled in the art without creative work are still within the scope of protection of the present disclosure.

Claims

1. The transient stability limit evaluation method of the new energy transmission system through flexible direct current is characterized by: include: Obtain the primary wiring topology of the new energy transmission system through flexible direct current, and establish a transient reduced-order linearization model of the new energy equipment, a transient reduced-order linearization model of the flexible direct current equipment, and a nonlinearization model of the new energy transmission system through flexible direct current according to the primary wiring topology; A system state matrix is ​​constructed according to the linearized model, a group of type-one equilibrium points is preliminarily determined according to the nonlinearized model, each target type-one equilibrium point is screened from the group of type-one equilibrium points through the system state matrix, and the first-order parameter matrix of the hypersection of each target type-one equilibrium point is calculated; Calculate the Hessian matrix according to the nonlinear model, and use the Hessian matrix to calculate the second-order parameter matrix of the hypersection of each target type-one equilibrium point; The corresponding hypersection surface equation is constructed according to the first-order parameter matrix and the second-order parameter matrix. The corresponding hypersection surface equation is constructed according to the fault trajectory and the first-order parameter matrix and the second-order parameter matrix. The intersection of the fault trajectory and the hypersection surface equation is determined, and the minimum value of the time of all the obtained intersection points is taken as the limit resection time of the fault.

2. The transient stability limit evaluation method of the new energy flexible direct current transmission system according to claim 1 is characterized in that: A transient reduced-order linearization model of new energy and flexible DC multi-device is established according to a primary wiring topology, including: the primary wiring topology is the controller parameters of the new energy and flexible DC devices and all basic data of the system operating conditions, the controller parameters of the new energy and flexible DC devices and all basic data of the system operating conditions are obtained, and the transient reduced-order linearization model of the new energy equipment and the flexible DC equipment is established according to all the acquired basic data, wherein, when establishing the transient reduced-order linearization model of the new energy equipment, only the dynamics of the phase-locked loop are considered, which is externally manifested as a current source characteristic, and the transient reduced-order linearization model of the new energy equipment is composed of differential equations and input-output interface equations; when establishing the transient reduced-order linearization model of the flexible DC equipment, only the virtual synchronous control link is considered, which is externally manifested as a voltage source characteristic, and the transient reduced-order linearization model of the flexible DC equipment is composed of differential equations and input-output interface equations.

3. The transient stability limit evaluation method of the new energy flexible direct current transmission system according to claim 1 is characterized in that: The system state matrix is ​​constructed according to the linearized model, including: the transient reduced-order linearized model of the combined new energy equipment, the transient reduced-order linearized model of the flexible DC equipment and the network equation, to obtain the system state matrix.

4. The transient stability limit evaluation method of the new energy flexible direct current transmission system according to claim 1 is characterized in that: The nonlinear model of the new energy via flexible direct current transmission system includes: establishing the nonlinear model of the new energy via flexible direct current transmission system according to the primary wiring topology, including: combining the nonlinear models of new energy equipment and flexible direct current equipment and network equations to obtain the nonlinear model of the new energy via flexible direct current transmission system.

5. The transient stability limit evaluation method of the new energy flexible direct current transmission system according to claim 1 is characterized in that: A set of type-one equilibrium points is preliminarily determined according to the nonlinear model, including: preliminarily calculating the unstable characteristic roots of the nonlinear model according to the definition that a type-one equilibrium point has only one unstable characteristic root, and using the unstable characteristic roots of the nonlinear model obtained by calculation as type-one equilibrium points.

6. The transient stability limit evaluation method of the new energy flexible direct current transmission system according to claim 4 is characterized in that: A target type-one equilibrium point is screened from a group of type-one equilibrium points through a system state matrix, and a first-order parameter matrix of a hypersection of each target type-one equilibrium point is calculated, including: from the preliminarily determined type-one equilibrium points, each preliminarily obtained type-one equilibrium point is screened through a system state matrix, and the eigenvalue is calculated according to the system state matrix to determine the target type-one equilibrium point; the left eigenvector corresponding to the unstable eigenroot of the target type-one equilibrium point is calculated, and the left eigenvector corresponding to the unstable eigenroot of each target type-one equilibrium point is used as the first-order parameter matrix of the hypersection equation of each target type-one equilibrium point.

7. The transient stability limit evaluation method of the new energy flexible direct current transmission system according to claim 1 is characterized in that: The second-order parameter matrix of the hypersection of each target type-one equilibrium point is calculated using the Hessian matrix to satisfy: Among them, Q is the second-order parameter matrix, The symbol represents the Kronecker tensor product, V c is the column stack map operation of the matrix, is the inverse operation of the matrix column stack map operation, I n represents the n-dimensional unit matrix, the coefficient matrices C and H are intermediate calculation matrices, J is the system state matrix, and H i is the Hessian matrix, y i is the left eigenvector corresponding to the unstable eigenvalue of the i-th target type-one equilibrium point, and μ is the value of the corresponding unstable eigenvalue.

8. The transient stability limit evaluation method of the new energy flexible direct current transmission system according to claim 1 is characterized in that: The corresponding hypersection equation is constructed based on the first-order parameter matrix and the second-order parameter matrix: Among them, x is the state variable fault trajectory, x u,i is the i-th target type-one equilibrium point; Q is the second-order parameter matrix; F i (x) is the hypertangent surface equation, y i is the transpose of the left eigenvector corresponding to the unstable eigenroot of the i-th target type-one equilibrium point.

9. The transient stability limit evaluation method of the new energy flexible direct current transmission system according to claim 6 is characterized in that: According to the fault trajectory and the first-order parameter matrix and the second-order parameter matrix, the corresponding hypersection surface equation is constructed to determine the intersection point between the fault trajectory and the hypersection surface equation, including: bringing the fault trajectory into any hypersection surface equation, when the function F of the hypersection surface equation i When the sign of the value of changes, it is considered that the fault trajectory passes through this hyper-tangent plane, that is, it satisfies: Among them, t i is the time corresponding to the intersection of the i-th target type-one equilibrium point and the fault trajectory in the hypersection equation, and Δt is the time step of the fault trajectory. Therefore, the minimum value of the time corresponding to all the obtained intersection points is taken as the limit removal time, which satisfies: t c =min(t1,t2,...,t i ) Among them, t c is the fault limit clearing time.

10. The transient stability limit evaluation system of the new energy flexible direct current transmission system is characterized by: include: A model building module is used to obtain the primary wiring topology of the new energy transmission system through flexible direct current, and to establish a transient reduced-order linearization model of the new energy equipment, a transient reduced-order linearization model of the flexible direct current equipment, and a nonlinear model of the new energy transmission system through flexible direct current according to the primary wiring topology; A first-order parameter determination module is used to construct a system state matrix according to a linearized model, preliminarily determine a group of type-one equilibrium points according to a nonlinearized model, select each target type-one equilibrium point from the group of type-one equilibrium points through the system state matrix, and calculate the first-order parameter matrix of the hypersection of each target type-one equilibrium point; A second-order parameter determination module is used to calculate the Hessian matrix according to the nonlinear model, and use the Hessian matrix to calculate the second-order parameter matrix of each target type-one equilibrium point hypersection; The quantitative evaluation module is used to construct the corresponding hyper-section surface equation according to the first-order parameter matrix and the second-order parameter matrix, to construct the corresponding hyper-section surface equation according to the fault trajectory and the first-order parameter matrix and the second-order parameter matrix, to determine the intersection of the fault trajectory and the hyper-section surface equation, and to take the minimum value of the time of all the obtained intersections as the limit removal time of the fault.

11. The transient stability limit evaluation system of the new energy flexible direct current transmission system according to claim 10, characterized in that: In the model building module, a transient reduced-order linearization model of new energy and flexible DC multi-device is established according to a primary wiring topology, including: the primary wiring topology is the controller parameters of the new energy and flexible DC devices and all basic data of the system operating conditions, the controller parameters of the new energy and flexible DC devices and all basic data of the system operating conditions are obtained, and the transient reduced-order linearization model of the new energy equipment and the flexible DC equipment is established according to all the acquired basic data, wherein, when establishing the transient reduced-order linearization model of the new energy equipment, only the dynamics of the phase-locked loop are considered, which is externally manifested as a current source characteristic, and the transient reduced-order linearization model of the new energy equipment is composed of differential equations and input-output interface equations; when establishing the transient reduced-order linearization model of the flexible DC equipment, only the virtual synchronous control link is considered, which is externally manifested as a voltage source characteristic, and the transient reduced-order linearization model of the flexible DC equipment is composed of differential equations and input-output interface equations.

12. The transient stability limit evaluation system of the new energy flexible direct current transmission system according to claim 11, characterized in that: The nonlinear model of the new energy via flexible direct current transmission system includes: establishing the nonlinear model of the new energy via flexible direct current transmission system according to the primary wiring topology, including: combining the nonlinear models of new energy equipment and flexible direct current equipment and network equations to obtain the nonlinear model of the new energy via flexible direct current transmission system.

13. The transient stability limit evaluation system of the new energy flexible direct current transmission system according to claim 10, characterized in that: In the first-order parameter determination module, a set of type-one equilibrium points is preliminarily determined according to the nonlinear model, including: based on the definition that a type-one equilibrium point has only one unstable characteristic root, the unstable characteristic root of the nonlinear model is preliminarily calculated, and the unstable characteristic root of the nonlinear model obtained by calculation is used as the type-one equilibrium point.

14. The transient stability limit evaluation system of the new energy flexible direct current transmission system according to claim 13, characterized in that: The target type-one equilibrium point is screened from a group of type-one equilibrium points through a system state matrix, and a first-order parameter matrix of a hypersection of each target type-one equilibrium point is calculated, including: based on the initially determined type-one equilibrium point, the initially determined type-one equilibrium point is screened through a system state matrix, and the eigenvalue is calculated according to the system state matrix to determine the target type-one equilibrium point; the left eigenvector corresponding to the unstable eigenroot of the target type-one equilibrium point is calculated, and the left eigenvector corresponding to the unstable eigenroot of each target type-one equilibrium point is used as the first-order parameter matrix of the hypersection equation of each target type-one equilibrium point.

15. The transient stability limit evaluation system of the new energy flexible direct current transmission system according to claim 10, characterized in that: In the second-order parameter determination module, the second-order parameter matrix of each target type-one equilibrium point hypersection is calculated using the Hessian matrix to satisfy: Among them, Q is the second-order parameter matrix, The symbol represents the Kronecker tensor product, V c is the column stack map operation of the matrix, is the inverse operation of the matrix column stack map operation, I n represents the n-dimensional identity matrix, the coefficient matrices C and H are intermediate calculation matrices, J is the system state matrix, and H i is the Hessian matrix, y i is the left eigenvector corresponding to the unstable eigenvalue of the i-th target type-one equilibrium point, and μ is the value of the corresponding unstable eigenvalue.

16. The transient stability limit evaluation system of the new energy flexible direct current transmission system according to claim 10, characterized in that: In the quantitative evaluation module, the corresponding hypersection equation is constructed according to the first-order parameter matrix and the second-order parameter matrix: Among them, x is the state variable fault trajectory, x u,i is the i-th target type-one equilibrium point; Q is the second-order parameter matrix; F i (x) is the hypertangent surface equation, y i is the transpose of the left eigenvector corresponding to the unstable eigenroot of the i-th target type-one equilibrium point.

17. The transient stability limit evaluation system of the new energy flexible direct current transmission system according to claim 10, characterized in that: According to the fault trajectory and the first-order parameter matrix and the second-order parameter matrix, the corresponding hypersection surface equation is constructed to determine the intersection point between the fault trajectory and the hypersection surface equation, including: bringing the fault trajectory into any hypersection surface equation, when the function F of the hypersection surface equation i When the sign of the value of changes, it is considered that the fault trajectory passes through this hyper-tangent plane, that is, it satisfies: Among them, t i is the time corresponding to the intersection of the i-th target type-one equilibrium point and the fault trajectory in the hypersection equation, and Δt is the time step of the fault trajectory. Therefore, the minimum value of the time corresponding to all the obtained intersection points is taken as the limit removal time, which satisfies: t c =min(t1,t2,...,t i ) Among them, t c is the fault limit clearing time.

18. A non-transitory computer-readable storage medium, characterized in that: The non-transitory computer-readable storage medium is used to store computer instructions. When the computer instructions are executed by the processor, the transient stability limit evaluation method of the new energy flexible direct current transmission system as described in any one of claims 1 to 9 is implemented.

19. An electronic device, characterized in that: include: A processor, a memory and a computer program; wherein the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device is running, the processor executes the computer program stored in the memory so that the electronic device executes the transient stability limit evaluation method for the new energy flexible direct current transmission system as described in any one of claims 1 to 9.

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